Configure SMB Multichannel behavior

In macOS Big Sur 11.3 and later, SMB Multichannel is enabled with default settings that are ideal for most organizations and users, but users can make adjustments as needed.

This article is intended for network administrators.

SMB Multichannel allows macOS to establish more than one connection to an SMB server, increase transfer speeds, and provide redundancy. The server must support SMB Multichannel to use any of these features.

To enable redundancy, you should enable more than one network connection that allows connectivity to the SMB server. When SMB Multichannel is enabled, and more than one network is available, macOS prefers the network that advertises itself to be the fastest. For macOS to use multiple connections simultaneously for faster transfer rates, the interfaces must have the same speeds enabled.

If you want to fully disable SMB Multichannel support in macOS, add the following line to the /etc/nsmb.conf file:

mc_on=no

Some Wi-Fi networks advertise faster speeds than the connected wired network. If you want to leave SMB Multichannel enabled and use Wi-Fi only as a failover for redundancy, because you prefer wired connections, add the following line to the /etc/nsmb.conf file:

mc_prefer_wired=yes

The /etc/nsmb.conf file doesn’t exist by default. To create one and apply both of the above changes, use the following Terminal commands:

echo "[default]" | sudo tee -a /etc/nsmb.conf

echo "mc_on=no" | sudo tee -a /etc/nsmb.conf

echo "mc_prefer_wired=yes" | sudo tee -a /etc/nsmb.conf

To revert the above changes, you can delete the /etc/nsmb.conf file safely.

For more information about the SMB Multichannel options supported on the active network, run the following Terminal command:

smbutil multichannel

Published Date: April 26, 2021

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